1. Field of the Invention
The present invention relates to an image taking apparatus such as a digital camera.
2. Description of the Related Art
Conventionally, as an automatic focusing (hereinafter, sometimes abbreviated as AF as required) technology for image taking apparatuses such as digital cameras, one has been known that, paying attention to a certain area of the image, evaluates the in-focus degree of the object by obtaining an evaluation value such as the contrast from the area. In this case, automatic focusing is performed by determining the lens position where the object image is in focus by detecting the lens position where the evaluation value is highest by stepwisely driving the taking lens. For such a technology, in order to accurately evaluate the focus condition of the object, it is desired to use an evaluation value that comparatively largely changes with the driving of the taking lens.
When automatic focusing is performed, there are cases where the object moves within the image plane during automatic focusing because of a camera movement or shake, or a movement of the object. For this reason, conventionally, the following has also been performed: the image planes of a plurality of images that are continuous in time are each divided into a plurality of area, and a movement of the object is detected by detecting an evaluation value change with time in each area. For such movement detection using an evaluation value for automatic focusing, in order to accurately detect a movement of the object within the image plane, it is desired that there be few image changes due to factors other than the movement of the object between the images for evaluating the movement of the object.
However, in the above-described movement detection, since a movement of the object within the image plane is detected by use of an evaluation value for automatic focusing, the driving of the taking lens is performed while a plurality of images for evaluating a movement of the object are obtained, so that the object movement detection is performed with images of different defocus amounts. Consequently, according to the conventional movement detection, a large evaluation value change occurs due to a defocus amount change as a factor other than a movement of the object, so that the possibility is high that a movement of the object is mis-detected.